1. Technical Field
The disclosure relates to bio-separation devices, and in particular, to magnetic separation units and magnetic separation devices capable of separating magnetic substances in bio-samples and methods for separating the magnetic substances in the bio-samples.
2. Description of the Related Art
In the field of biology, many efficient techniques for separating one type of cell or a class of cells from a complex cell suspension are disclosed and have wide applications. The ability to remove certain cells from a clinical blood sample that are indicative of a particular disease state could be useful as a diagnostic tool for better understanding the particular state of the disease.
It has been shown that cells tagged with micron sized (>1 μm) magnetic or magnetized particles can be successfully removed or separated from mixtures by using magnetic devices. For the removal of the desired cells, i.e., cells which provide valuable information, a desired cell population is magnetized and removed from a complex liquid mixture (so-called positive selection or positive separation). In an alternative method, the undesirable cells, i.e., cells that may prevent or alter the results of a particular procedure are magnetized and subsequently removed with a magnetic device (so-called negative selection or negative separation).
Cell separation methods utilizing magnetic tags are mainly divided into two kinds, wherein one kind is the so-called column-based separation method which uses magnetic particles with a smaller size or a weaker magnetic magnetization as tags, and separates these tags in a column filled with magnetic fillers. High magnetic gradients are generated close to the surfaces of the magnetic fillers when a magnetic field is applied to the column. The other kind is the so-called tube-based separation method using a centrifugal tube as a separation vessel. The magnetic tags are separated within a centrifugal tube by magnetic field generated by a magnet outside the tube. Therefore, larger sized tags or stronger magnetic magnetization are needed for separation efficiency. Note that for the tube-based separation method there is no need to use a column with magnetic fillers, like the column-based separation method.
However, separation efficiency of the magnetic cells depends on the magnetic forces acting on the magnetic tags. Thus, an increase in the magnetic field or magnetic field gradient improves separation efficiency. However, whether using permanent magnets or electromagnets, the magnetic field and magnetic field gradient decrease as the distance increases. Therefore, separation efficiency of the magnetic cells in conventional centrifugal tubes is difficult to improve, because high magnetic filed and high magnetic field gradient cannot be applied to magnetic materials in the conventional tubes.